Maggie Yihong Chen

All ink-jet-printed carbon nanotube thin-film transistor on a polyimide substrate with an ultrahigh operating frequency of over 5 GHz

We report a flexible carbon nanotube (CNT) thin-film transistor (TFT) fabricated solely by ink-jet printing technology. The TFT is top gate configured, consisting of source and drain electrodes, a carrier transport layer based on an ultrapure, high-density (>1000 CNTs/μm2) CNT thin film, an ion-gel gate dielectric layer, and a poly(3,4-ethylenedioxythiophene) top gate electrode. All the TFT elements are ink-jet printed at room temperature on a polyimide substrate without involving any photolithography patterning or surface pretreatment steps. This CNT-TFT exhibits a high operating frequency of over 5 GHz and an on-off ratio of over 100. Such an all-ink-jet-printed process eliminates the need for lithography, vacuum processing, and metallization procedures and thus provides a promising technology for low-cost, high-throughput fabrication of large-area high-speed flexible electronic circuits on virtually any desired flexible substrate.

Dispersion-enhanced photonic crystal fiber array for a true time-delay structured X-band phased array antenna

Tunable optical true time-delay modules based on highly dispersive photonic crystal fibers (PCFs) are demonstrated to provide continuous radio-frequency squint-free beam scanning for an X-band (8-12 GHz) phased array antenna system. The dispersion of the fabricated PCF is as high as -600 ps/nm /spl middot/ km at 1550 nm. The time delay is continuously tunable from -31 to 31 ps between adjacent delay lines by tuning the laser wavelength continuously from 1528 to 1560 nm. The far field radiation patterns of a 1/spl times/4 subarray were measured from -45/spl deg/ to 45/spl deg/ scanning angles. Squint-free operation is experimentally confirmed.

Inkjet-Printed Two-Dimensional Phased-Array Antenna on a Flexible Substrate

In this letter, we present a two-dimensional 2-bit 4 × 4 phased-array antenna on a flexible Kapton substrate fabricated using inkjet printing. Printed carbon nanotube thin-film transistors (CNT-TFTs) form the switching elements in the phase-shifting network. A multilayer interconnection scheme has been utilized to fully package the subsystem and enable convenient access of the control lines to the 64 CNT-TFTs. By appropriately controlling the on and off states of the TFT switches using a computer mainframe, beam steering of a 5-GHz RF signal at four steering angles of θ = 0^°, φ = 0^°; θ = 14.5^°, φ = 0^°; θ = 20.7^°, φ = -45^°; and θ = 34^°, φ = -26.5^° are experimentally demonstrated. The insertion loss and the power consumption by the switch array are measured to be 8.17 dB and 11.2 mW, respectively .

Photonic Crystal Fiber-Based True-Time-Delay Beamformer for Multiple RF Beam Transmission and Reception of an X-Band Phased-Array Antenna

We report multiple beam transmission and reception of an X-band phased antenna array utilizing highly dispersive photonic crystal fiber (PCF), which has a dispersion value of - 600 ps/nm/km at 1550 nm, as true-time-delay (TTD) elements. In the transmission mode, two RF signals with frequencies 8.4 and 12 GHz are simultaneously steered at angles 7.4 and 21.2 degrees, respectively. In the receiving mode experiment, two RF signals with frequencies 8.4 and 12 GHz impinging upon an X-band antenna array from angles -7.4 and -21.2 degrees, respectively, are detected and the angles of arrival are determined accurately. Many RF beams can be simultaneously transmitted or received. The demonstration is only limited by the hardware availability and the bandwidth of the wavelength differentiation capability of the system.

Design of a broadband highly dispersive pure silica photonic crystal fiber

A highly dispersive dual-concentric-core pure silica photonic crystal fiber is designed with a maximum chromatic dispersion value of about -9500 ps/(nm km) around the 1.56 microm wavelength region and a full width at half-maximum (FWHM) of 55 nm. The change in the dispersion-bandwidth product as a function of period is carefully studied by using the plane wave expansion method. The coupled mode theory matches well with the plane wave expansion method that was used to simulate the chromatic dispersion. This kind of a photonic crystal fiber structure is suitable for high-dispersion application in phased array antenna systems based on photonic crystal fiber arrays.

Photonic Crystal Fiber Beamformer for Multiple

A multiple-beam optical beamformer based on highly dispersive photonic crystal fibers (PCFs) is presented. Each radio-frequency (RF) beam can be independently controlled to steer continuously. The dispersion of the fabricated PCFs is as high as -600 ps/nmldrkm at 1550 nm. Simultaneous two-beam transmission is demonstrated using two lasers with different optical wavelengths. The two wavelengths generate two independent sets of time delays, which correspond to two independent RF beams.

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A 4-bit polymer optoelectronic true-time delay (TTD) device is demonstrated. The planar lightwave circuit (PLC) is composed of monolithically integrated low-loss passive polymer waveguide delay lines and five cascaded 2 times 2 polymer thermooptic switches. Waveguide junction offsets and air trenches simultaneously reduce the bending loss and device area. Simulations are used to optimize the trench and offset structures for fabrication. The 16 time delays generated by the device are measured to be in the range from 0 to 177 ps in 11.8-ps increments. The packaged PLC has an insertion loss of up to 14.9 dB, and the delay switching speed is 2 ms. An eight-element X-band phased-array antenna system is constructed to demonstrate the beam-steering capabilities of the 4-bit-delay devices. The TTD devices are shown to steer the far-field radiation pattern between 0deg and -14.5deg

-Band Phased-Array Antenna Transmissions

A fully integrated 4-bit true time delay device using polymer optical switches and waveguide delay lines is demonstrated. The fabricated device, which contains five 2x2 thermo-optic switches, has a maximum power consumption of 143 mW and a switching time less than 3 ms. The rf phase error, which is affected by the optical switch cross talk, is also theoretically analyzed and proved to be negligible by experimental results.

Reconfigurable Delay Time Polymer Planar Lightwave Circuit for an X-band Phased-Array Antenna Demonstration

The optimal design of a polymer-based thermooptic (TO) switch using a total internal reflection (TIR) effect is proposed to improve switching performance. Numerical calculations show that this type of optical switch can achieve an ultrabroad optical bandwidth as well as a low polarization dependent loss. The devices fabricated with different half branch angles consume driving powers from 25 to 66 mW. The switches also show fiber-to-fiber insertion losses at 2.8 dB and polarization dependent losses (PDLs) at 0.2 dB. The measured rising and falling times are 1.5 and 2 ms, respectively. The optical bandwidth of the devices, which is limited by the material absorption from the fluorinated polymer, is quite large extending from 630 to 1630 nm

Phase error corrected 4-bit true time delay module using a cascaded 2 × 2 polymer waveguide switch array

Hybrid photonic true-time delay modules for phased-array antennas are designed and demonstrated. Continuously tunable true-time delay network based on highly dispersive photonic bandgap fiber (up to 2135 ps/nm/km at 1570 nm), combined with a programmable true-time delay network utilizing optical waveguide delay line and optical switches, provides the antenna with quasi-continuous steering ability. Far-field patterns are simulated and measured to confirm the squint-free beam steering.